Search

Natural sediments are often mixtures of cohesive and non-cohesive sediment, and there are few data on the specific behaviour of these sediments, in particular, their erodibility. After a brief synthesis of recent works on the erosion threshold and the erosion rate of non-cohesive, cohesive and mixed sediments, the erodimetre, a new erosion device developed by IFREMER, is described. The instrument is portable and enables the separate quantification of the erosion of mud and sand fractions. Four data sets are presented, consisting of erosion tests on pure sands, laboratory mixtures with two types of mud and well-sorted sands, and natural mixed sediments. A clear relationship between the critical shear stress for erosion and the mud volume fraction (over the whole range) is shown. The correlation is not so good with the clay fraction. When the sand is fine (140 μm), the relationship is linear. When the sand size increases (280 μm), a sharp transition from non-cohesive to cohesive behaviour appears when the mud fraction exceeds 35-40%. It is suggested that the ratio between the grain sizes of the sand and the fine fractions, and more generally the whole size spectrum of the sediment, should be considered to characterise the sediment erodibility. This first interpretation extends the conceptual framework for the erosion behaviour described by Van Ledden et al. (2004). [ABSTRACT FROM AUTHOR]